Replacing polyacrylonitrile with Kraft lignin for sustainable carbon fiber manufacturing mitigates carbon emissions†

Although carbon fibers have been significantly sought after as the foundation of various advanced materials, their manufacturing is energy-intensive with high carbon emissions. Replacing the petroleum-derived polyacrylonitrile (PAN) precursor of carbon fibers with green biopolymers can potentially enhance the sustainability of the carbon fiber industry, but how this replacement can mitigate carbon emissions is still elusive. In this study, we performed a life cycle assessment (LCA) on the alternative of a plant-derived lignin biopolymer from biorefining waste for the replacement of PAN in carbon fiber production. Here, 50% of PAN was replaced with an industrial softwood Kraft lignin, and wet spinning was used for making lignin/PAN precursor fibers, followed by thermostabilization and carbonization. LCA study revealed that carbon fibers made from PAN could induce carbon emissions of 23.3 kg CO₂-eq per kg carbon fibers, while 50% replacement of PAN with lignin led to carbon emissions of 19.5 kg CO₂-eq per kg carbon fibers, representing a 16.3% reduction in carbon emissions. Analysis of the main contributions to carbon emissions from processing demonstrated that the preparation of spinning dopes had the highest carbon emission, followed by thermostabilization, wet spinning, and carbonization. Among the different production factors, consumed electricity generated the highest carbon emissions, followed by the precursor PAN. Among other environmental impacts, electricity represented the highest contributor, and the preparation of spinning dopes had the most environmental impacts. Further sensitivity analysis elucidated that increasing the spinning tow and carbon yield led to lower carbon emissions and other environmental impacts. All these results highlighted that using lignin instead of PAN could significantly mitigate carbon emissions for greener carbon fiber production.